The book of Law that Chrisitans follow is the Bible
God created Adam and Eve in his own image. By disobedience, they fell from their sinless state through the temptation by Satan. This fall plunged humanity into a state of sin and spiritual death, and brought upon the entire race the sentence of eternal death. From this condition we can be saved only by the grace of God, through faith, on the basis of the work of Christ, and by the agency of the Holy Spirit.